Application of tree ring analysis to paleoseismology

Knowledge of a region's seismicity is one of the keys to estimating earthquake hazards. Unfortunately, historical records are generally inadequate for evaluations of seismicity. Paleoseismology addresses this problem using various techniques for dating earthquake-disturbed materials. Trees, with widespread distribution, identifiable annual growth increments, and sensitivity to environmental change, can provide a unique tool for dating past earthquake events. Geomorphic and hydrologic changes and dynamic stress resulting from earthquakes can cause a variety of effects in individual trees and communities of trees. Tree ring analysis can (1) produce the actual year and sometimes the season for disturbance events and (2) establish synchroneity for events that may be beyond the range of absolute calendar dating. Tree ring dating, or dendrochronology, is used to establish exact dates based on patterns of annual ring variations through time. Mere counting of rings is inadequate and may lead to errors because of possible missing, micro or false rings. Trees ranging in age from 300 to 500 years grow in many places and can be used to identify previously unknown seismic disturbances or to better define events that are partially known. Longer time spans can be covered in some instances. Earthquakes may be more precisely located in space and time or have their magnitudes better estimated by analysis of tree rings. A number of studies have established the validity of tree ring application to paleoseismology but only a few studies have contributed new information to the paleoseismic record. The science should now move from the discovery phase to a wider application phase. Successful applications will add important information to the records of seismicity and the evaluation of earthquake hazards.